1. The Solar Oblateness Measured On Board The PICARD Spacecraft,
and The Solar Disk Sextant Instrument
Gérard Thuillier1, Alain1 Hauchecorne1, Sabatino Sofia2, Terry Girard2,
Jean-François Hochedez1, Abdenour Irbah1, Jean-Pierre Marcovici1,
Mireille Meissonnier1, Mustapha Meftah1, Ulysses Sofia1, and the PICARD team
1 LATMOS-CNRS (F), 2 Yale University (US), 3 American University (US) .
OUTLINE
(1) Title
(2) PICARD Mission
(3) and (4) SODISM instrument
(5) Why and how to measure the solar oblateness?
(6) Method
(7) Results
(8) SDS instrument
(9) SDS results
(10) The Yale Convective Zone model
(11) Comparison and discussion
(12) Conclusion

2. THE PICARD mission LATMOS (F) Yale University IRMB (B) GSFC PMOD (Ch)
OCA
Meudon Obs.
Nice University
IAS
LMD
DAPNIA-CEA
Yale University
GSFC
JPL
NRL
CSA / EC
ILWS
PICARD was launched on 15 June 2010 in a sun synchronous orbit. It consists of a microsatellite carrying four instruments: two radiometers (PREMOS and SOVAP), a bolometric sensor and an imaging telescope (SODISM).
Two other presentations will be given on PICARD: to complete with the reference

3. SODISM INSTRUMENT (2)
SODISM instrument is an imaging telescope observing in four wavelength domains equipped with a 2 K x 2 K CCD detector. The payload is actively pointed on the Sun with 0.2 arcsecond accuracy
The wavelenghts are chosen in the solar photospheric continuum and in the Ca II line at 393 nm to monitor the occurrence of active regions.

4. SODISM OPTICAL SCHEMATICS
Sun
Image generated by the telescope
Image on the CCD
Image after the
annular mirror
primary mirror
Image at the guiding focus
4 guiding
detectors
Interference filters
4 prisms
Entrance
window
SODISM OPTICAL SCHEMATICS

5. Why and how to measure the solar oblateness?
Why: The solar oblateness is the result of the internal rotation of the Sun. As a
consequence, it can test the rotation properties determined from helioseismology.
In addition, it determines the quadrupole moment of the Sun, responsible for
producing the advance of Mercury’s perihelion. Since this phenomenon is due
to general relativistic effects, the measurement is also important for basic
physics.
How: The oblateness measurements are obtained during special operations in which
the spacecraft turns around the Sun direction. The rotation, made by 30° angular
increments, allows us to determine the instrument optical distortion and
the solar oblateness.

6. PICARD/SODISM

7. SODISM Oblateness Determination

8. SODISM Oblateness Results (preliminary)
90°
135°
45°
MDO 535 DL:
Ang Oblateness
± 1.2 x10-6
± 1.2
± 1.1
± 1.2
MDO 535 RS:
± 1.9 x10-6
± 1.7
± 1.4
± 1.6
MDO 782 DL:
± 1.2 x10-6
± 1.0
± 1.0
± 0.9 0°

9. Solar Disk Sextant (SDS)

10. SDS Oblateness Determination

11. THE YALE MODEL OF THE SOLAR INTERIOR
TWO-DIMENSIONAL STRUCTURE AND EVOLUTION
EMPHASIS ON CONVECTION ZONE
INCLUDES MAGNETIC FIELDS, DIFFUSION, ROTATION, AND TURBULENCE
HIGH PRECISION TO BE ABLE TO HANDLE WITH SMALL CHANGE
MOST ACCURATE MICRO-PHYSICS CURRENTLY AVAILABLE
OBJECTIVES
TO DETERMINE THE PHYSICAL MECHANISM FOR SOLAR VARIABILITY
WITH CLIMATE CONSEQUENCES, BY MEASURING W=dlnR/dlnL, and
DETERMINING THE INTERNAL SOLAR CONFIGURATIONS THAT LEAD TO IT.
USE W AND OLD VALUES OF R (MEASURED e.g. FROM SOLAR ECLIPSES, TO DETERMINE PAST VALUES OF THE SOLAR LUMINOSITY.

12. COMPARISON AND DISCUSSION

13. CONCLUSION
References:

14. Not fpr use in the presentation (part of the submitted abstract)
SODISM, an imaging telescope with a 2K x 2K CCD detector, is dedicated to the measurement of the solar diameter and the limb shape. Although the data processing is still in a validation phase, we already present some preliminary results concerning the solar oblateness.
These measurements are obtained during a special operation in which the spacecraft turns around the Sun direction. The rotation, made by 300 angular increments, allows us to determine the instrument optical distortion and the solar oblateness. The method used to extract this information will be described. We shall present the preliminary results as a function of wavelength, and compare them with measurements obtained with the SDS instrument, and with the predictions from theoretical modeling